Perennial plants such as long-lived trees and woody plants have a life style considerably different from annual plants, such as Arabidopsis, in that perennial plants such as trees has an indeterminate growth, whereas plants such as Arabidopsis terminate growth when the plant flowers.
Perennial plants can also cycle between periods of active growth and dormancy. The lifecycle of long-lived trees and woody plants differs significantly from annual crops, which often translocate carbon and nitrogen to seeds. Due to these differences between annual crops and perennial plants, such as trees, it has in many instances been found that a model system such as Populus tremula x tremuloides is a superior system for reliably finding genes, which can be used for increasing biomass production in woody plants.
Plant growth at apical meristems results in the development of sets of primary tissues and in the lengthening of the stem and roots. In addition to this primary growth, trees undergo secondary growth and produce secondary tissue “wood” from the cambium. This secondary growth increases the girth of stems and roots.
There are several factors such as different gene products that might need to be altered in order to enhance biomass production in trees. Growth in height, diameter, stem volume and wood density are important traits to follow for increased growth and biomass production. In view of the need to provide perennial plants capable of enhanced growth and biomass in a range of different environmental conditions, as well as changing environmental conditions, there is a continual need to provide plants with different genetic traits (comprising different sets of active genes) that adapt the plants for growth under these conditions.
In general, high yield plants can be made by crossing different lines, selecting plants with the best growing properties, where seeds from these plants can then be selected and new crosses can be performed. In this process, plants with better growth properties can be identified. One problem with trees and woody plants is that they need to be several years old before they produce flowers and can be used for traditional crossing. This can be overcome by using various molecular biology techniques.
This invention describes how expression of a set of genes can be altered to create transgenic woody plants, which have improved growth properties, improved biomass and higher yield compared to the corresponding non-genetically modified wild type woody plant.